Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $106.60   11.188%   $118.5264   $118.53   $118.55   $118.50  
  Purchase #2 $166.81   4.470%   $174.2664   $174.27   $174.25   $174.30  
  Purchase #3 $40.47   11.523%   $45.1334   $45.13   $45.15   $45.10  
  Purchase #4 $195.92   10.367%   $216.231   $216.23   $216.25   $216.20  
  Purchase #5 $68.89   8.849%   $74.9861   $74.99   $75.00   $75.00  
  Purchase #6 $57.81   10.640%   $63.961   $63.96   $63.95   $64.00  
  Purchase #7 $215.85   11.494%   $240.6598   $240.66   $240.65   $240.70  
  7 purchase totals = $852.35       $933.7641   $933.77   $933.80   $933.80